Solder sealing in high-power laser devices

ABSTRACT

In various embodiments, laser apparatuses include thermal bonding layers between various components and sealing materials for preventing or retarding movement of thermal bonding material out of the thermal bonding layers.

RELATED APPLICATION

This application claims the benefit of and priority to U.S. ProvisionalPatent Application No. 62/108,278, filed Jan. 27, 2015, the entiredisclosure of which is hereby incorporated herein by reference.

TECHNICAL FIELD

In various embodiments, the present invention relates to laser devicessuch as laser diodes, specifically apparatus and methods for sealingthermal bonding layers in laser devices.

BACKGROUND

High-power laser systems are utilized for a host of differentapplications, such as welding, cutting, drilling, and materialsprocessing. Such laser systems typically include a laser emitter, thelaser light from which is coupled into an optical fiber (or simply a“fiber”), and an optical system that focuses the laser light from thefiber onto the workpiece to be processed. Wavelength beam combining(WBC) is a technique for scaling the output power and brightness fromlaser diodes, laser diode bars, stacks of diode bars, or other lasersarranged in a one- or two-dimensional array. WBC methods have beendeveloped to combine beams along one or both dimensions of an array ofemitters. Typical WBC systems include a plurality of emitters, such asone or more diode bars, that are combined using a dispersive element toform a multi-wavelength beam. Each emitter in the WBC systemindividually resonates, and is stabilized through wavelength-specificfeedback from a common partially reflecting output coupler that isfiltered by the dispersive element along a beam-combining dimension.Exemplary WBC systems are detailed in U.S. Pat. No. 6,192,062, filed onFeb. 4, 2000, U.S. Pat. No. 6,208,679, filed on Sep. 8, 1998, U.S. Pat.No. 8,670,180, filed on Aug. 25, 2011, and U.S. Pat. No. 8,559,107,filed on Mar. 7, 2011, the entire disclosure of each of which isincorporated by reference herein.

While techniques such as WBC have succeeded in producing laser-basedsystems for a wide variety of applications, wider adoption of suchsystems has resulted in the demand for ever-higher levels of laseroutput power. Typically higher laser powers involve the driving of laserdiodes at increasingly higher currents, which results in higheroperating temperatures and concomitant thermal-management issues aimedat preventing temperature-based reliability issues. One such issue issolder creep. High-power lasers typically feature the use of a laseremitter with one or more heat sinks or other thermal-managementstructures for heat dissipation, and these structures are often coupledto the emitter via a solder or other soft, malleable compound thatmaintains thermal contact between the emitter and heat sink even in theevent of relative movement between the components resulting from thermalcycling.

While such solder-based solutions mitigate some of the reliabilityissues resulting from thermal cycling during high-power laser operation,the use of solder may also introduce other reliability issues such assolder creep. During solder creep, the solder develops internal voidsthat can coalesce and lead to crack nucleation. In addition, the soldermay slowly work its way out from between the two mating surfaces. Thisproblem is exacerbated by the fact that the components between which thesolder is placed are typically clamped or screwed together in order tosqueeze the components together and minimize any thermal distortion.This clamping force may increase the solder-creep rate, particularlyduring high-temperature operation when the solder is typically softerand more flowable.

Thus, there is a need for structures and methods that mitigate creep ofsolder or other flowable joining compounds in high-power laser devices.

SUMMARY

In accordance with embodiments of the present invention, laser devicesincorporating beam emitters such as laser diodes (e.g., single laserdiodes, laser diode bars, or arrays thereof) incorporate a thermalbonding material (e.g., a solder or similar material) that is sealed toprevent creep of the thermal bonding material, thereby enhancing thermalconductivity within the laser device and the reliability of the laserdevice. Specifically, thermal bonding layers between various componentsof the laser device (e.g., the beam emitter itself and/or heat-sinkingcomponents such as electrode mounts and housings) may be sealed with amaterial (e.g., one or more metals) that is impervious to thepropagation of the thermal bonding material therethrough; thus, creep ofthe thermal bonding material from between the components issubstantially prevented. The sealing may be accomplished by, forexample, a deposition technique such as electroplating or electrolessdeposition. In embodiments of the present invention in which the thermalbonding material is disposed between the beam emitter and one or moreelectrode mounts, the sealing may be performed before or after the beamemitter is affixed to the electrode mount(s) via the thermal bondingmaterial. Portions of the laser device where the sealing material is notdesired (e.g., portions of the beam emitter from which the beam(s) areemitted) may be protected from deposition of the sealing material via,e.g., masking or the selective application of an inhibitor material thatprevents deposition thereon. In other embodiments, such portions of thelaser device may initially be coated with the sealing material, and thesealing material may be later removed via, e.g., etching and/ormachining.

In accordance with embodiments of the present invention, laser devicesmay also be thermally managed via a package that incorporates highlythermally and electrically conductive electrodes for driving the beamemitter, as well as a thermally conductive mount (that may be liquidcooled) that is electrically isolated from the electrodes. Specifically,the electrodes may include, consist essentially of, or consist of copperand be electrically connected to the anode and cathode of the beamemitter. The mount may include, consist essentially of, or consist of,e.g., aluminum, and may incorporate an electrically insulating layerbetween the mount and the electrode facing the mount. For example, theelectrically insulating layer may include, consist essentially of, orconsist of aluminum oxide and/or aluminum nitride layers that providethermal conductivity therethrough but retard or substantially preventelectrical conduction therethrough. Aluminum nitride advantageously hasa high thermal conductivity but a low electrical conductivity. Asutilized herein, materials with a high thermal conductivity, or“thermally conductive materials,” have a thermal conductivity of atleast 100 watts per meter per Kelvin (W·m⁻¹·K⁻¹), at least 170W·m⁻¹·K⁻¹, or even at least 300 W·m⁻¹·K⁻¹. As utilized herein, materialswith a high electrical conductivity, or “electrically conductivematerials,” have an electrical conductivity, e.g., at 20° C., of atleast 1×10⁵ siemens per meter (S/m), at least 1×10⁶ S/m, or even atleast 1×10⁷ S/m. As utilized herein, materials with a high electricalresistivity, or “electrically insulating materials,” have an electricalresistivity of at least 1×10⁸ ohm·meter (Ω·m), at least 1×10¹⁰ Ω·m, oreven at least 1×10¹² Ω·m.

Laser devices in accordance with embodiments of the present inventionmay be utilized in WBC systems to form high brightness, low beamparameter product (BPP) laser systems. The BPP is the product of thelaser beam's divergence angle (half-angle) and the radius of the beam atits narrowest point (i.e., the beam waist, the minimum spot size). TheBPP quantifies the quality of the laser beam and how well it can befocused to a small spot, and is typically expressed in units ofmillimeter-milliradians (mm-mrad). A Gaussian beam has the lowestpossible BPP, given by the wavelength of the laser light divided by pi.The ratio of the BPP of an actual beam to that of an ideal Gaussian beamat the same wavelength is denoted M², or the “beam quality factor,”which is a wavelength-independent measure of beam quality, with the“best” quality corresponding to the “lowest” beam quality factor of 1.

As known to those of skill in the art, lasers are generally defined asdevices that generate visible or invisible light through stimulatedemission of light. Lasers generally have properties that make themuseful in a variety of applications, as mentioned above. Common lasertypes include semiconductor lasers, solid-state lasers, fiber lasers,and gas lasers. Semiconductor lasers (mostly laser diodes) may beelectrically or optically pumped and generally efficiently generate veryhigh output powers often at the expense of poor beam quality.Semiconductor lasers may produce low power with good spatial propertiesfor application in, e.g., optical disc players. Yet other semiconductorlasers may be suitable for producing high pulse rate, low power pulses(e.g., for telecommunications applications). Special types ofsemiconductor lasers include quantum cascade lasers (for mid-infraredlight) and surface-emitting semiconductor lasers (VCSELs and VECSELs),the latter also being suitable for pulse generation with high powers.

Solid-state lasers may be based on ion-doped crystals or glasses (e.g.,doped insulator lasers) and may pumped with discharge lamps or laserdiodes for generating high output power. Alternatively solid-statelasers may produce low power output with very high beam quality,spectral purity and/or stability (e.g. for measurement purposes). Somesolid-state lasers may produce ultra-short pulses with picosecond orfemtosecond durations. Common gain media for use with solid state lasersinclude: Nd:YAG, Nd:YVO₄, Nd:YLF, Nd:glass, Yb:YAG, Yb:glass,Ti:sapphire, Cr:YAG, and Cr:LiSAF.

Fiber lasers may be based on optical glass fibers which are doped withsome laser-active ions in the fiber core. Fiber lasers may achieveextremely high output powers (up to kilowatts) with high beam quality.Narrow line width operation and the like may also be supported by fiberlasers. Gas lasers, which include helium-neon lasers, CO₂ lasers, argonion lasers, and the like, may be based on gases which are typicallyexcited with electrical discharges. Frequently used gases include CO₂,argon, krypton, and gas mixtures such as helium-neon. In addition,excimer lasers may be based on any of ArF, KrF, XeF, and F₂. Other lesscommon laser types include chemical and nuclear pumped lasers, freeelectron lasers, and X-ray lasers.

A laser diode, such as a laser diode described in the following generaldescription may be used in association with embodiments of theinnovations described herein. A laser diode is generally based on asimple diode structure that supports the emission of photons (light).However, to improve efficiency, power, beam quality, brightness,tunability, and the like, this simple structure is generally modified toprovide a variety of many practical types of laser diodes. Laser diodetypes include small edge-emitting varieties that generate from a fewmilliwatts up to roughly half a watt of output power in a beam with highbeam quality. Structural types of diode lasers include doubleheterostructure lasers that include a layer of low bandgap materialsandwiched between two high bandgap layers; quantum well lasers thatinclude a very thin middle layer (quantum well layer) resulting in highefficiency and quantization of the laser's energy; multiple quantum welllasers that include more than one quantum well layer improve gaincharacteristics; quantum wire or quantum sea (dots) lasers replace themiddle layer with a wire or dots that produce higher efficiency quantumwell lasers; quantum cascade lasers that enable laser action atrelatively long wavelengths that may be tuned by altering the thicknessof the quantum layer; separate confinement heterostructure lasers, whichare the most common commercial laser diode and include another twolayers above and below the quantum well layer to efficiently confine thelight produced; distributed feedback lasers, which are commonly used indemanding optical communication applications and include an integrateddiffraction grating that facilitates generating a stable wavelength setduring manufacturing by reflecting a single wavelength back to the gainregion; vertical-cavity surface-emitting lasers (VCSELs), which have adifferent structure that other laser diodes in that light is emittedfrom its surface rather than from its edge; and vertical-external-cavitysurface-emitting-laser (VECSELs) and external-cavity diode lasers, whichare tunable lasers that use mainly double heterostructure diodes andinclude gratings or multiple-prism grating configurations.External-cavity diode lasers are often wavelength-tunable and exhibit asmall emission line width. Laser diode types also include a variety ofhigh power diode-based lasers including: broad area lasers that arecharacterized by multi-mode diodes with oblong output facets andgenerally have poor beam quality but generate a few watts of power;tapered lasers that are characterized by astigmatic mode diodes withtapered output facets that exhibit improved beam quality and brightnesswhen compared to broad area lasers; ridge waveguide lasers that arecharacterized by elliptical mode diodes with oval output facets; andslab-coupled optical waveguide lasers (SCOWL) that are characterized bycircular mode diodes with output facets and may generate watt-leveloutput in a diffraction-limited beam with nearly a circular profile.

Laser diode arrays, bars and/or stacks, such as those described in thefollowing general description may be used in association withembodiments of the innovations described herein. Laser diodes may bepackaged individually or in groups, generally in one-dimensionalrows/arrays (diode bars) or two dimensional arrays (diode-bar stacks). Adiode array stack is generally a vertical stack of diode bars. Laserdiode bars or arrays generally achieve substantially higher power, andcost effectiveness than an equivalent single broad area diode.High-power diode bars generally contain an array of broad-area emitters,generating tens of watts with relatively poor beam quality; despite thehigher power, the brightness is often lower than that of a broad arealaser diode. High-power diode bars may be stacked to produce high-powerstacked diode bars for generation of extremely high powers of hundredsor thousands of watts. Laser diode arrays may be configured to emit abeam into free space or into a fiber. Fiber-coupled diode-laser arraysmay be conveniently used as a pumping source for fiber lasers and fiberamplifiers.

A diode-laser bar is a type of semiconductor laser containing aone-dimensional array of broad-area emitters or alternatively containingsub arrays containing, e.g., 10-20 narrow stripe emitters. A broad-areadiode bar typically contains, for example, 19-49 emitters, each havingdimensions on the order of, e.g., 1 μm×100 μm. The beam quality alongthe 1 μm dimension or fast-axis is typically diffraction-limited. Thebeam quality along the 100 μm dimension or slow-axis or array dimensionis typically many times diffraction-limited. Typically, a diode bar forcommercial applications has a laser resonator length of the order of 1to 4 mm, is about 10 mm wide and generates tens of watts of outputpower. Most diode bars operate in the wavelength region from 780 to 1070nm, with the wavelengths of 808 nm (for pumping neodymium lasers) and940 nm (for pumping Yb:YAG) being most prominent. The wavelength rangeof 915-976 nm is used for pumping erbium-doped or ytterbium-dopedhigh-power fiber lasers and amplifiers.

A property of diode bars that is usually addressed is the output spatialbeam profile. For most applications beam conditioning optics are needed.Significant efforts are therefore often required for conditioning theoutput of a diode bar or diode stack. Conditioning techniques includeusing aspherical lenses for collimating the beams while preserving thebeam quality. Micro optic fast axis collimators may be used to collimatethe output beam along the fast-axis. Arrays of aspherical cylindricallenses are often used for collimation of each laser element along thearray or slow-axis. To achieve beams with approximately circular beamwaist, a special beam shaper for symmetrization of the beam quality ofeach diode bar or array can be applied. A degrading property of diodebars is the “smile”—a slight bend of the planar nature of the connectedemitters. Smile errors may have detrimental effects on the ability tofocus beams from diode bars. Another degrading property is collimationerror of the slow- and fast-axis. For example, a twisting of thefast-axis collimation lens results in an effective smile. This hasdetrimental effects on the ability to focus. In stacks, “pointing” errorof each bar is often the most dominant effect. Pointing error is acollimation error and is the result of the array or bar that is offsetfrom the fast-axis lens. An offset of 1 μm is the same as the wholearray having a smile of 1 μm.

Diode bars and diode arrays overcome limitations of very broad singleemitters, such as amplified spontaneous emission or parasitic lasing inthe transverse direction or filament formation. Diode arrays may also beoperated with a more stable mode profile, because each emitter producesits own beam. Techniques which exploit some degree of coherent couplingof neighbored emitters may result in better beam quality. Suchtechniques may be included in the fabrication of the diode bars whileothers may involve external cavities. Another benefit of diode arrays isthat the array geometry makes diode bars and arrays very suitable forcoherent or spectral beam combining to obtain a much higher beamquality.

In addition to raw bar or array offerings, diode arrays are available infiber-coupled form because this often makes it much easier to utilizeeach emitter's output and to mount the diode bars so that cooling of thediodes occurs some distance from the place where the light is used.Usually, the light is coupled into a single multimode fiber, usingeither a simple fast-axis collimator without beam conditioning in theslow-axis direction, or a more complex beam shaper to better preservethe brightness. It is also possible to launch the beamlets from theemitters into a fiber bundle (with one fiber per emitter). Emissionbandwidth of a diode bar or diode array is an important considerationfor some applications. Optical feedback (e.g. from volume Bragg grating)can significantly improve wavelength tolerance and emission bandwidth.In addition, bandwidth and exact center wavelength may also be importantfor spectral beam combining.

A diode stack is simply an arrangement of multiple diode bars that candeliver very high output power. Also called diode laser stack, multi-barmodule, or two-dimensional laser array, the most common diode stackarrangement is that of a vertical stack which is effectively atwo-dimensional array of edge emitters. Such a stack may be fabricatedby attaching diode bars to thin heat sinks and stacking these assembliesso as to obtain a periodic array of diode bars and heat sinks. There arealso horizontal diode stacks, and two-dimensional stacks. For high beamquality, the diode bars generally should be as close to each other aspossible. On the other hand, efficient cooling requires some minimumthickness of the heat sinks mounted between the bars. This tradeoff ofdiode bar spacing results in beam quality of a diode stack in thevertical direction (and subsequently its brightness) much lower thanthat of a single diode bar. There are, however, several techniques forsignificantly mitigating this problem, e.g., by spatial interleaving ofthe outputs of different diode stacks, by polarization coupling, or bywavelength multiplexing. Various types of high-power beam shapers andrelated devices have been developed for such purposes. Diode stacks mayprovide extremely high output powers (e.g. hundreds or thousands ofwatts).

Embodiments of the present invention couple the one or more input laserbeams into an optical fiber. In various embodiments, the optical fiberhas multiple cladding layers surrounding a single core, multiplediscrete core regions (or “cores”) within a single cladding layer, ormultiple cores surrounded by multiple cladding layers.

Herein, “optical elements” may refer to any of lenses, mirrors, prisms,gratings, and the like, which redirect, reflect, bend, or in any othermanner optically manipulate electromagnetic radiation. Herein, beamemitters, emitters, or laser emitters, or lasers include anyelectromagnetic beam-generating device such as semiconductor elements,which generate an electromagnetic beam, but may or may not beself-resonating. These also include fiber lasers, disk lasers, non-solidstate lasers, etc. Generally, each emitter includes a back reflectivesurface, at least one optical gain medium, and a front reflectivesurface. The optical gain medium increases the gain of electromagneticradiation that is not limited to any particular portion of theelectromagnetic spectrum, but that may be visible, infrared, and/orultraviolet light. An emitter may include or consist essentially ofmultiple beam emitters such as a diode bar configured to emit multiplebeams. The input beams received in the embodiments herein may besingle-wavelength or multi-wavelength beams combined using varioustechniques known in the art. In addition, references to “lasers,” “laseremitters,” or “beam emitters” herein include not only single-diodelasers, but also diode bars, laser arrays, diode bar arrays, and singleor arrays of vertical cavity surface-emitting lasers (VCSELs).

In an aspect, embodiments of the invention feature a laser apparatusthat includes or consists essentially of a beam emitter having first andsecond opposed surfaces, a first electrode mount disposed proximate(e.g., beneath) the first surface of the beam emitter, a thermal bondinglayer, and a sealing material. The thermal bonding layer is disposed atan interface between the first electrode mount and the first surface ofthe beam emitter. The thermal bonding layer improves thermal conductionbetween the first electrode mount and the beam emitter. The thermalbonding layer includes, consists essentially of, or consists of athermal bonding material. The sealing material is disposed along atleast a portion of the interface between the first electrode mount andthe first surface of the beam emitter. The sealing material may bedisposed around substantially the entire interface between the firstelectrode mount and the first surface of the beam emitter. The sealingmaterial may be disposed over, or even in mechanical contact with, alateral surface of the thermal bonding layer (e.g., the thermal bondingmaterial). Portions of the sealing material may be in mechanical contactwith the first electrode mount and/or the beam emitter. The sealingmaterial may prevent or retard movement of the thermal bonding materialout of the thermal bonding layer (i.e., movement of the thermal bondingmaterial from between the first electrode mount and the beam emitter).The sealing material may prevent or retard the formation of voids withinthe thermal bonding material and/or the thermal bonding layer.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The beam emitter may include orconsist essentially of one or more diode bars each emitting a pluralityof discrete beams (e.g., laser beams). The thermal bonding material mayinclude, consist essentially of, or consist of indium or an alloy ormixture of indium with one or more metals. The sealing material mayinclude, consist essentially of, or consist of copper, aluminum, nickel,and/or chromium or an alloy or mixture of two or more of those metals oran alloy of mixture of one of those metals with one or more othermetals. The sealing material may be disposed over at least a portion ofthe external surface of the first electrode mount (i.e., the surface(s)of the first electrode mount not facing and/or in contact with thethermal bonding layer and/or the beam emitter). The sealing material maybe disposed over substantially the entire external surface of the firstelectrode mount. The sealing material may be disposed over at least aportion of the external surface of the beam emitter (i.e., thesurface(s) of the beam emitter not facing and/or in contact with thethermal bonding layer and/or the first electrode mount). The sealingmaterial may be disposed over substantially the entire external surfaceof the beam emitter. The sealing material may not be disposed over theportion of the external surface of the beam emitter from which thebeam(s) is/are emitted.

A second electrode mount may be disposed proximate (e.g., over) thesecond surface of the beam emitter. The second electrode mount may beelectrically insulated from the first electrode mount. The secondelectrode mount may be in electrical contact with the second surface ofthe beam emitter. A second thermal bonding layer may be disposed at aninterface between the second electrode mount and the second surface ofthe beam emitter. The second thermal bonding layer may include, consistessentially of, or consist of a second thermal bonding material. Asecond sealing material may be disposed along at least a portion of theinterface between the second electrode mount and the second surface ofthe beam emitter. The second sealing material may be disposed aroundsubstantially the entire interface between the second electrode mountand the second surface of the beam emitter. The second sealing materialmay be disposed over, or even in mechanical contact with, a lateralsurface of the second thermal bonding layer (e.g., the second thermalbonding material). Portions of the second sealing material may be inmechanical contact with the second electrode mount and/or the beamemitter. The second sealing material may prevent or retard movement ofthe second thermal bonding material out of the second thermal bondinglayer (i.e., movement of the second thermal bonding material frombetween the second electrode mount and the beam emitter). The secondsealing material may prevent or retard the formation of voids within thesecond thermal bonding material and/or the second thermal bonding layer.The thermal bonding material and the second thermal bonding material mayinclude, consist essentially of, or consist of the same material. Thethermal bonding material and the second thermal bonding material mayinclude, consist essentially of, or consist of different materials. Thesecond sealing material may include, consist essentially of, or consistof copper, aluminum, nickel, and/or chromium or an alloy or mixture oftwo or more of those metals or an alloy of mixture of one of thosemetals with one or more other metals. The second sealing material may bedisposed over at least a portion of the external surface of the secondelectrode mount (i.e., the surface(s) of the second electrode mount notfacing and/or in contact with the second thermal bonding layer and/orthe beam emitter). The second sealing material may be disposed oversubstantially the entire external surface of the second electrode mount.The second sealing material may be disposed over at least a portion ofthe external surface of the beam emitter (i.e., the surface(s) of thebeam emitter not facing and/or in contact with the second thermalbonding layer and/or the second electrode mount). The second sealingmaterial may be disposed over substantially the entire external surfaceof the beam emitter. The second sealing material may not be disposedover the portion of the external surface of the beam emitter from whichthe beam(s) is/are emitted.

The first electrode mount may be in electrical contact with the firstsurface of the beam emitter. The first and/or second electrode mount mayinclude, consist essentially of, or consist of copper, silver, or gold.The housing body may include, consist essentially of, or consist ofaluminum. The housing body may define therewithin one or more coolingchannels for the flow of cooling fluid (e.g., water or anotherheat-transfer liquid) therethrough.

In another aspect, embodiments of the invention feature a method ofsealing a laser apparatus. A thermal bonding layer is disposed over asurface of an electrode mount (e.g., a heat sink). The thermal bondinglayer includes, consists essentially of, or consists of a thermalbonding material. A sealing material is deposited over at least aportion of the thermal bonding layer and at least a portion of anexternal surface of the electrode mount. A beam emitter is disposed indirect contact with the thermal bonding layer. At least a portion of thesealing material is positioned to prevent or retard movement of thethermal bonding material out of the thermal bonding layer (i.e.,movement of the thermal bonding material from between the electrodemount and the beam emitter).

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The beam emitter may be disposed indirect contact with the thermal bonding layer before the sealingmaterial is deposited. The beam emitter may be disposed in directcontact with the thermal bonding layer after the sealing material isdeposited. The sealing material may be disposed along at least a portionof the interface between the electrode mount and the beam emitter. Thesealing material may be disposed around substantially the entireinterface between the electrode mount and the beam emitter. The sealingmaterial may be disposed over, or even in mechanical contact with, alateral surface of the thermal bonding layer (e.g., the thermal bondingmaterial). Portions of the sealing material may be in mechanical contactwith the electrode mount and/or the beam emitter. The sealing materialmay include, consist essentially of, or consist of copper, aluminum,nickel, and/or chromium or an alloy or mixture of two or more of thosemetals or an alloy of mixture of one of those metals with one or moreother metals. The sealing material may be disposed over at least aportion of the external surface of the electrode mount (i.e., thesurface(s) of the electrode mount not facing and/or in contact with thethermal bonding layer and/or the beam emitter). The sealing material maybe disposed over substantially the entire external surface of theelectrode mount. The sealing material may be disposed over at least aportion of the external surface of the beam emitter (i.e., thesurface(s) of the beam emitter not facing and/or in contact with thethermal bonding layer and/or the electrode mount). The sealing materialmay be disposed over substantially the entire external surface of thebeam emitter. The sealing material may not be disposed over the portionof the external surface of the beam emitter from which the beam(s)is/are emitted. The beam emitter may include or consist essentially ofone or more diode bars each emitting a plurality of discrete beams(e.g., laser beams). The thermal bonding material may include, consistessentially of, or consist of indium or an alloy or mixture of indiumwith one or more metals.

Before the beam emitter is disposed in direct contact with the thermalbonding layer, a portion of the sealing material may be removed toreveal an exposed portion of the thermal bonding layer. The beam emittermay be disposed in direct contact with the exposed portion of thethermal bonding layer (i.e., disposing the beam emitter in directcontact with the thermal bonding layer may include or consistessentially of disposing the beam emitter in direct contact with theexposed portion of the thermal bonding layer). A portion of the thermalbonding layer may be covered (e.g., coated) with a masking materialbefore depositing the sealing material. After the sealing material isdeposited, at least a portion of the masking material may be removedbefore disposing the beam emitter in direct contact with the thermalbonding layer. Depositing the sealing material may include, consistessentially of, or consist of electroplating and/or electrolessdeposition. The beam emitter may be disposed in contact with the thermalbonding layer before the thermal bonding layer is disposed on theelectrode mount (e.g., the thermal bonding layer may be applied to thebeam emitter before the coated beam emitter is disposed in contact withthe electrode mount.

In yet another aspect, embodiments of the invention feature a method ofsealing a laser apparatus. A thermal bonding layer is disposed over asurface of an electrode mount. The thermal bonding layer includes,consists essentially of, or consists of a thermal bonding material. Abeam emitter is disposed in contact (e.g., direct mechanical contact)with the thermal bonding layer. Thereafter, a sealing material isdeposited over at least a portion of the thermal bonding layer and atleast a portion of an external surface of the electrode mount (i.e., thesurface(s) of the electrode mount not facing and/or in contact with thethermal bonding layer and/or the beam emitter). The sealing material maybe deposited over a portion of the beam emitter (e.g., a portion of thebeam emitter proximate the thermal bonding layer). At least a portion ofthe sealing material is positioned to prevent or retard movement of thethermal bonding material out of the thermal bonding layer (i.e.,movement of the thermal bonding material from between the electrodemount and the beam emitter).

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The beam emitter may be disposed incontact with the thermal bonding layer before the thermal bonding layeris disposed on the electrode mount (e.g., the thermal bonding layer maybe applied to the beam emitter before the coated beam emitter isdisposed in contact with the electrode mount. The sealing material maybe disposed along at least a portion of the interface between theelectrode mount and the beam emitter. The sealing material may bedisposed around substantially the entire interface between the electrodemount and the beam emitter. The sealing material may be disposed over,or even in mechanical contact with, a lateral surface of the thermalbonding layer (e.g., the thermal bonding material). Portions of thesealing material may be in mechanical contact with the beam emitter. Thesealing material may include, consist essentially of, or consist ofcopper, aluminum, nickel, and/or chromium or an alloy or mixture of twoor more of those metals or an alloy of mixture of one of those metalswith one or more other metals. The sealing material may be disposed oversubstantially the entire external surface of the electrode mount. Thesealing material may be disposed over at least a portion of the externalsurface of the beam emitter (i.e., the surface(s) of the beam emitternot facing and/or in contact with the thermal bonding layer and/or theelectrode mount). The sealing material may be disposed oversubstantially the entire external surface of the beam emitter. Thesealing material may not be disposed over the portion of the externalsurface of the beam emitter from which the beam(s) is/are emitted. Thebeam emitter may include or consist essentially of one or more diodebars each emitting a plurality of discrete beams (e.g., laser beams).The thermal bonding material may include, consist essentially of, orconsist of indium or an alloy or mixture of indium with one or moremetals.

The sealing material may be deposited over at least a portion of thebeam emitter. At least a portion of the sealing material may be removedto reveal a portion of the beam emitter (e.g., the portion of the beamemitter from which the beam(s) is/are emitted). One or more portions ofthe beam emitter and/or the electrode mount may be covered with amasking material before the sealing material is deposited. At least someof the masking material may be removed after depositing the sealingmaterial. Depositing the sealing material may include, consistessentially of, or consist of electroplating and/or electrolessdeposition.

In another aspect, embodiments of the invention feature a wavelengthbeam combining laser system that includes or consists essentially of abeam emitter, focusing optics, a dispersive element, a partiallyreflective output coupler, a first electrode mount disposed proximate(e.g., beneath) the first surface of the beam emitter, a thermal bondinglayer disposed at an interface between the first electrode mount and thefirst surface of the beam emitter, and a sealing material disposed alongat least a portion of the interface between the first electrode mountand the first surface of the beam emitter. The beam emitter emits aplurality of discrete beams (e.g., laser beams) and has first and secondopposed surfaces. The focusing optics focus the plurality of beams ontothe dispersive element. The distance between the dispersive element andthe focusing optics may approximately correspond to a focal length ofthe focusing optics (in other embodiments, this distance is less than orgreater than the focal length of the focusing optics). The dispersiveelement receives and disperses the received focused beams. The partiallyreflective output coupler is positioned to receive the dispersed beams,transmit a portion of the dispersed beams therethrough (i.e., throughthe output coupler, e.g., toward a workpiece to be processed with orsubjected to the multi-wavelength beam) as a multi-wavelength outputbeam, and reflect a second portion of the dispersed beams back towardthe dispersive element. The thermal bonding layer improves thermalconduction between the first electrode mount and the beam emitter. Thethermal bonding layer includes, consists essentially of, or consists ofa thermal bonding material. The sealing material may prevent or retardmovement of the thermal bonding material out of the thermal bondinglayer (i.e., movement of the thermal bonding material from between thefirst electrode mount and the housing body). The sealing material mayprevent or retard the formation of voids within the thermal bondingmaterial and/or the thermal bonding layer.

Embodiments of the invention may include one or more of the following inany of a variety of combinations. The dispersive element may include orconsist essentially of a diffraction grating (e.g., a reflective gratingor a transmissive grating). The thermal bonding material may include,consist essentially of, or consist of indium or an alloy or mixture ofindium with one or more metals. The sealing material may include,consist essentially of, or consist of copper, aluminum, nickel, and/orchromium or an alloy or mixture of two or more of those metals or analloy of mixture of one of those metals with one or more other metals. Asecond electrode mount may be disposed proximate (e.g., over) the secondsurface of the beam emitter. The second electrode mount may beelectrically insulated from the first electrode mount. The secondelectrode mount may be in electrical contact with the second surface ofthe beam emitter. A second thermal bonding layer may be disposed at aninterface between the second electrode mount and the second surface ofthe beam emitter. The second thermal bonding layer may include, consistessentially of, or consist of a second thermal bonding material. Asecond sealing material may be disposed along at least a portion of theinterface between the second electrode mount and the second surface ofthe beam emitter. The second sealing material may be disposed aroundsubstantially the entire interface between the second electrode mountand the second surface of the beam emitter. The second sealing materialmay be disposed over, or even in mechanical contact with, a lateralsurface of the second thermal bonding layer (e.g., the second thermalbonding material). Portions of the second sealing material may be inmechanical contact with the second electrode mount and/or the beamemitter. The second sealing material may prevent or retard movement ofthe second thermal bonding material out of the second thermal bondinglayer (i.e., movement of the second thermal bonding material frombetween the second electrode mount and the beam emitter). The secondsealing material may prevent or retard the formation of voids within thesecond thermal bonding material and/or the second thermal bonding layer.The thermal bonding material and the second thermal bonding material mayinclude, consist essentially of, or consist of the same material. Thethermal bonding material and the second thermal bonding material mayinclude, consist essentially of, or consist of different materials. Thesecond sealing material may include, consist essentially of, or consistof copper, aluminum, nickel, and/or chromium or an alloy or mixture oftwo or more of those metals or an alloy of mixture of one of thosemetals with one or more other metals. The second sealing material may bedisposed over at least a portion of the external surface of the secondelectrode mount (i.e., the surface(s) of the second electrode mount notfacing and/or in contact with the second thermal bonding layer and/orthe beam emitter). The second sealing material may be disposed oversubstantially the entire external surface of the second electrode mount.The second sealing material may be disposed over at least a portion ofthe external surface of the beam emitter (i.e., the surface(s) of thebeam emitter not facing and/or in contact with the second thermalbonding layer and/or the second electrode mount). The second sealingmaterial may be disposed over substantially the entire external surfaceof the beam emitter. The second sealing material may not be disposedover the portion of the external surface of the beam emitter from whichthe beam(s) is/are emitted.

The first electrode mount may be in electrical contact with the firstsurface of the beam emitter. The first and/or second electrode mount mayinclude, consist essentially of, or consist of copper, silver, or gold.The housing body may include, consist essentially of, or consist ofaluminum. The housing body may define therewithin one or more coolingchannels for the flow of cooling fluid (e.g., water or anotherheat-transfer liquid) therethrough.

These and other objects, along with advantages and features of thepresent invention herein disclosed, will become more apparent throughreference to the following description, the accompanying drawings, andthe claims. Furthermore, it is to be understood that the features of thevarious embodiments described herein are not mutually exclusive and mayexist in various combinations and permutations. As used herein, theterms “substantially” and “approximately” mean±10%, and in someembodiments, ±5%. The term “consists essentially of” means excludingother materials that contribute to function, unless otherwise definedherein. Nonetheless, such other materials may be present, collectivelyor individually, in trace amounts. Herein, the terms “radiation” and“light” are utilized interchangeably unless otherwise indicated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIGS. 1 and 2 are, respectively, a side view and a perspective view of apackaged laser in accordance with embodiments of the invention;

FIGS. 3 and 4 are side views of packaged lasers in accordance withembodiments of the invention;

FIGS. 5A-5D are cross-sectional views of components of laser devicesundergoing various steps of a sealing process in accordance withembodiments of the invention;

FIGS. 6A and 6B are cross-sectional views of components of laser devicesundergoing various steps of a sealing process in accordance withembodiments of the invention; and

FIG. 7 is a schematic view of a wavelength beam combining laser systemincorporating a packaged laser in accordance with embodiments of theinvention.

DETAILED DESCRIPTION

FIGS. 1 and 2 depict portions of an exemplary packaged laser 100 inaccordance with embodiments of the present invention. As shown, thelaser 100 includes a beam emitter 105 sandwiched between two electrodemounts 110, 115. The beam emitter 105 may include or consist essentiallyof, e.g., a laser diode, a diode bar, an array of laser diodes, an arrayof diode bars, or one or more vertical cavity surface-emitting lasers(VCSELs). The electrode mounts 110, 115 are thermally connected to thebeam emitter 105 and each electrically connected to one of theelectrodes (i.e., the anode and the cathode) of the beam emitter 105.For example, the electrode mount 110 may be electrically connected tothe anode of beam emitter 105 and the electrode mount 115 may beelectrically connected to the cathode of beam emitter 105, or viceversa. The electrode mounts 110, 115 are typically highly thermally andelectrically conductive; thus, in various embodiments, the electrodemounts 110, 115 include, consist essentially of, or consist of one ormore metals such as copper, silver, or gold. An insulating layer 120 isdisposed around the beam emitter 105 and between the electrode mounts110, 115, thereby electrically isolating the electrode mounts 110, 115from each other. As shown, the electrode mounts 110, 115 may be fastenedtogether and to the beam emitter 105 via, e.g., one or more fastenerssuch as screws, which may also attach the electrode mounts to a housing(as detailed below). Conductive contacts 125, 130 are connected to andextend from the electrode mounts 110, 115 in order to facilitateinterconnection of the laser 100 to, for example, other laser devices(in series or in parallel) or to a source of electrical power (e.g., acurrent source). Laser 100 may also incorporate one or more featuresdescribed in, and/or be fabricated in accordance with, U.S. Pat. No.9,178,333, filed on Mar. 24, 2015, the entire disclosure of which isincorporated herein by reference.

FIG. 3 depicts a laser device 300 in which one or both electrode mounts110, 115 are fastened or affixed to a thermally conductive housing 310.The housing 310 may include or consist essentially of a housing body 315capped with an insulating layer 320 that retards or substantiallyprevents electrical conduction between the electrode mount 110 and thehousing body 315 while maintaining thermal conductivity therebetween.For example, the insulating layer 320 may include, consist essentiallyof, or consist of aluminum nitride, boron arsenide, diamond, and/orberyllium oxide. In some embodiments, the insulating layer 320 may notbe present. The housing body 315 may include, consist essentially of, orconsist of one or more thermally conductive metals or ceramic materials.In an embodiment, the housing body 315 includes, consists essentially,or consists of a thermally conductive metal such as aluminum or copper.As shown in FIG. 3, the housing body 315 may also incorporatetherewithin one or more cooling channels 325 through which a coolant(e.g., a liquid such as water) may flow to remove heat from the housingbody. A coolant source and coolant sink may be connected to the coolingchannel 325 via coolant interconnections 330. A coolant reservoir and,e.g., a heat exchanger, may be fluidly connected to the cooling channel325 and provide coolant thereto. Such cooling systems are conventionaland may be utilized with embodiments of the present invention withoutundue experimentation.

The insulating layer 320 may include, consist essentially of, or consistof, e.g., an oxide or a nitride of the metal of which the housing body315 is composed. For example, for a housing body 315 that includes,consists essentially of, or consists of aluminum, the insulating layer320 may include, consist essentially of, or consist of one or morelayers of aluminum oxide and/or aluminum nitride. In some embodiments, athermal bonding layer 335 is utilized to enhance contact (and thusthermal conduction) between the electrode mount 110 and the housing 310,even if the insulating layer 320 has a rough surface. The thermalbonding layer 335 may include, consist essentially of, or consist of,for example, a thermal bonding material such as a thermally conductivesolder, foil, liquid, paste, or gel material such as indium (e.g.,indium paste or solder) or silver paste. The thickness of the thermalbonding layer 335 may be, for example, between approximately 0.5 μm andapproximately 150 μm. The thickness of the insulating layer 320 may be,for example, between approximately 5 μm and approximately 150 μm. Invarious embodiments, a thermal bonding layer 335 may also be presentbetween the beam emitter 105 and one or both of the electrode mounts110, 115. As described in more detail below, thermal bonding layers 335and/or portions of components in contact therewith may be sealed with asealing material in accordance with embodiments of the present inventionto minimize or prevent creep of the thermal bonding layer 335. Thermalbonding layers and laser devices in accordance with embodiments of theinvention may also incorporate one or more structures or systems forinhibiting movement of thermal bonding material as described in U.S.Provisional Patent Application No. 62/108,250, filed Jan. 27, 2015, theentire disclosure of which is incorporated by reference herein.

All or a portion of the insulating layer 320 may be a nitride layerformed via, e.g., direct nitridation of the housing body 315 and/orcarbothermic reduction of an oxide layer on housing body 315. Forexample, an insulating layer 320 (or a topmost insulating layer 320)that includes, consists essentially of, or consists of aluminum nitridemay be formed via exposure of an aluminum housing body 315 (or analuminum oxide layer thereon) to a nitrogen ambient (i.e., a surroundingenvironment including nitrogen or a nitrogen-containing species) atelevated temperature (e.g., greater than 1200° C.). An aluminum oxideinsulating layer 320 may be formed on an aluminum housing body 315 via,e.g., anodization. In an exemplary anodization process, the housing body315 is first cleaned in either a hot soak cleaner or in a solvent bathand may be etched in sodium hydroxide (normally with added sodiumgluconate), ammonium bifluoride, or brightened in a mix of acids. Theanodized layer may be produced by passing a direct current through anelectrolytic solution, with the housing body 315 serving as the anode(the positive electrode). The current releases hydrogen at the cathode(the negative electrode) and oxygen at the surface of the housing body315 anode, creating a build-up of aluminum oxide. The voltage utilizedfor various solutions may range from 1 to 300 V DC, although most fallin the range of 15 to 21 V. Higher voltages are typically required forthicker coatings formed in sulfuric and organic acid. The anodizingcurrent varies with the area of housing body 315 being anodized, andtypically ranges from 30 to 300 amperes/meter² (2.8 to 28 ampere/ft²).

In some embodiments, anodizing of aluminum housing bodies 315 isperformed in an acid solution which slowly dissolves the aluminum oxide.The acid action is balanced with the oxidation rate to form a coatingwith nanopores 10-150 nm in diameter. These pores allow the electrolytesolution and current to reach the aluminum surface and continueproducing the coating to greater thickness beyond what is produced byautopassivation. In some embodiments, these pores are sealed in order toprevent air or water from reaching the housing body 315 and initiatingcorrosion. In one implementation, a crystallized, partiallycrystallized, or micro-crystalline filler is placed into the pores, asdisclosed in U.S. Pat. Nos. 8,512,872 and 8,609,254, the entiredisclosure of each of which is incorporated by reference herein.

Pores in an insulating layer 320 may be at least partially impregnatedor filled by introducing one or more compounds that are at leastpartially resistant to acidic attack or alkaline attack under variousconditions. For example, the one or more compounds (e.g., metal cationicspecies) may be introduced into the pores by immersion of the housingbody 315 in a bath containing one or more precursor compounds underconditions that are non-reactive to the housing body 315 or an oxidethereof. In accordance with various embodiments of the invention, thehousing body 315, which may include, consist essentially of, or consistof anodized aluminum or an anodized aluminum alloy, is immersed in afirst aqueous metal salt solution, preferably at ambient conditions. Inaddition or instead, one or more metal cationic species may beintroduced into at least some of the pores by, for example, immersingthe housing body 315 in an aqueous metal solution. The metal species orbase metal salt in solution may at least partially impregnate at least aportion of the anodic oxide pores by diffusion phenomena. Non-limitingexamples of the metal that may be utilized as a precursor compoundinclude nickel, iron, zinc, copper, magnesium, titanium, zirconium,aluminum, and silver. The bath or aqueous metal solution may have a pHof less than about 7 and a temperature in a range of from about 15° C.to about 35° C.

FIG. 4 depicts a packaged laser 400 featuring a composite housing 410electrically insulated from but thermally connected to the electrodemount 110 of laser 100. As shown, the composite housing 410 may featurea ceramic body 415 mounted on and/or affixed to housing body 315. Theceramic body 415 may be thermally connected to electrode mount 110and/or to housing body 315 via one or more thermal bonding layers 335therebetween. The ceramic body 415 may include, consist essentially of,or consist of, for example, aluminum nitride. As shown in FIG. 4, theceramic body 415 may also have interfacial layers 420 on one or moresurfaces thereof. For example, the interfacial layers 420 may improvethermal conductivity to the bulk of the ceramic body 415 via increasedinterfacial contact (due to, e.g., reduced surface roughness) to thethermal bonding layers 335. The interfacial layers 420 may include,consist essentially of, or consist of one or more thermally conductivemetals such as copper, silver, or gold. For example, the interfaciallayers 420 may include, consist essentially of, or consist ofdirect-bond copper or copper flashing disposed on the ceramic body 415.

As mentioned above, various embodiments of the present invention featuresealing materials to minimize or reduce creep of one or more thermalbonding layers. FIG. 5A depicts electrode mounts 110, 115 each with athermal bonding layer 335 disposed thereon. As mentioned above, athermal bonding layer 335 may include, consist essentially of, orconsist of a thermal bonding material. The thermal bonding material mayinclude, consist essentially of, or consist of, for example, a thermallyconductive solder, foil, liquid, paste, or gel material that includes,consists essentially of, or consists of one or more materials such asindium, lead, tin, silver, and/or an alloy thereof. The thermal bondingmaterial may have a melting point between, e.g., approximately 90° C.and approximately 450° C., between approximately 100° C. andapproximately 250° C., or between approximately 140° C. andapproximately 200° C. As shown in FIG. 5D, the thermal bonding layers335 provide a thermal connection between the electrode mounts 110, 115and the beam emitter 105. (Although FIGS. 5A-5D depict both electrodemounts 110, 115 being at least partially sealed and subsequentlythermally connected to beam emitter 105, embodiments of the inventioninclude laser devices in which only one of electrode mounts 110, 115 isutilized.)

As shown in FIG. 5B, each of the electrode mounts 110, 115 with thethermal bonding layer 335 applied thereto may be at least partiallysealed with a sealing material 500 to prevent creep of the thermalbonding material from areas between the beam emitter 105 and theelectrode mounts. The sealing material 500 may extend aroundsubstantially the entire surface area of the electrode mount andassociated thermal bonding layer 335. The sealing material 500 isgenerally substantially impervious to transport of the thermal bondingmaterial therethrough, and therefore substantially prevents egress ofthe thermal bonding material in the assembled laser device. The sealingmaterial 500 may include, consist essentially of, or consist of one ormore metals, e.g., thermally conductive metals, and it may have amelting point higher than that of the thermal bonding layer 335 (e.g.,of the thermal bonding material). For example, the sealing material 500may include, consist essentially of, or consist of copper, aluminum,nickel, chromium, or an alloy of two or more of those metals or one ormore of those metals with one or more other metals. The sealing material500 may have a hardness higher than that of the thermal bondingmaterial. In various embodiments, the sealing material 500 and thethermal bonding material are substantially mutually insoluble (i.e., nomore than approximately 10%, or even no more than approximately 5%, ofthe sealing material 500 or the thermal bonding material may dissolveinto the other to form a solid solution), at least at temperatures oftypical operation of the assembled laser device (e.g., temperaturesreached by components in contact with the thermal bonding material) orlower.

The sealing material 500 may be applied to the electrode mounts andthermal bonding layers via any of a variety of different techniques. Forexample, the sealing material 500 may be deposited by a technique suchas electroplating, electroless deposition, chemical vapor deposition, orsputtering. In an electroplating process in accordance with embodimentsof the invention, as known in the art, the component to be sealed isimmersed in a bath containing ions of the sealing material 500 and/or ananode including, consisting essentially of, or consisting of the sealingmaterial 500, and an applied current results in the deposition of theions onto the component, which acts as the cathode. In an electrolessdeposition process in accordance with embodiments of the invention, asknown in the art, the electroplating current source is absent, and thebath contains a reducing agent (e.g., a hydrogen-based reducer such ashypophosphite or a low molecular weight aldehyde) that drives theplating reaction.

In various embodiments of the invention one or more portions of thesealing material 500 may be removed from the electrode mount and/or thethermal bonding layer 335. As shown in FIG. 5C, portions of the sealingmaterial 500 may be removed from the thermal bonding layers 335 whichare intended to directly contact the beam emitter in the assembled laserdevice, thereby forming exposed regions 510. As shown in FIG. 5D, thebeam emitter 105 may be disposed between sealed electrode mounts 110,115 such that it directly contacts the thermal bonding layers 335(thereby ensuring good thermal contact) while the remaining portions ofthe sealing material 500 prevent egress of the thermal bonding materialfrom the interfaces between the beam emitter 105 and the electrodemounts 110, 115. The portions of the sealing material 500 on regions 510may be removed by, e.g., etching (for example, where other regions ofthe sealing material 500 are masked by a protective layer inert to theetchant) or mechanical removal methods such as machining or grinding.

In other embodiments of the invention, the sealing material 500 is notformed on the regions 510 during the initial sealing process. In suchembodiments, regions 510 may be initially covered or coated with amasking material such as wax, tape, etc. The sealing material 500 is notdeposited on the masked-off regions 510, and after the depositingprocess (e.g., electroplating or electroless deposition), the maskingmaterial is simply removed to reveal regions 510 as shown in FIG. 5C.

As shown in FIG. 6A, in accordance with embodiments of the presentinvention, various components of the laser device may be assembledtogether before application of the sealing material. As shown, theelectrode mounts 110, 115 may be affixed to the beam emitter 105 withthermal bonding layers 335 therebetween prior to the application of thesealing material. As shown in FIG. 6B, the sealing material 500 may beapplied to the entire assembly shown in FIG. 6A, thereby sealing thethermal bonding layers 335 and preventing egress of the thermal bondingmaterial during operation of the laser device. As detailed above,exposed portions of the beam emitter 105 may either be masked off,thereby preventing any deposition of the sealing material 500, or thesealing material 500 may be deposited on such areas and subsequentlyremoved by, e.g., etching or mechanical removal techniques.

Packaged lasers in accordance with embodiments of the present inventionmay be utilized in WBC laser systems. FIG. 7 depicts an exemplary WBClaser system 700 that utilizes a packaged laser 705. The packaged laser705 may correspond to, for example, lasers 100, 300, or 400 as detailedherein, and may incorporate, for example, one or more thermal bondinglayers 335 and a sealing material 500 as detailed herein. In the exampleof FIG. 7, laser 705 features a diode bar having four beam emittersemitting beams 710 (see magnified input view 715), but embodiments ofthe invention may utilize diode bars emitting any number of individualbeams or two-dimensional arrays or stacks of diodes or diode bars. Inview 715, each beam 710 is indicated by a line, where the length orlonger dimension of the line represents the slow diverging dimension ofthe beam, and the height or shorter dimension represents the fastdiverging dimension. A collimation optic 720 may be used to collimateeach beam 710 along the fast dimension. Transform optic(s) 725, whichmay include or consist essentially of one or more cylindrical orspherical lenses and/or mirrors, are used to combine each beam 710 alonga WBC direction 730. The transform optics 725 then overlap the combinedbeam onto a dispersive element 735 (which may include or consistessentially of, e.g., a diffraction grating such as a reflective ortransmissive diffraction grating), and the combined beam is thentransmitted as single output profile onto an output coupler 740. Theoutput coupler 740 then transmits the combined beams 745 as shown on theoutput front view 750. The output coupler 740 is typically partiallyreflective and acts as a common front facet for all the laser elementsin this external cavity system 700. An external cavity is a lasingsystem where the secondary mirror is displaced at a distance away fromthe emission aperture or facet of each laser emitter. In someembodiments, additional optics are placed between the emission apertureor facet and the output coupler or partially reflective surface.

The terms and expressions employed herein are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

What is claimed is:
 1. A laser apparatus comprising: a beam emitterhaving first and second opposed surfaces; a first electrode mountdisposed proximate the first surface of the beam emitter; a thermalbonding layer disposed at an interface between the first electrode mountand the first surface of the beam emitter, the thermal bonding layer (i)improving thermal conduction between the first electrode mount and thebeam emitter, and (ii) comprising a thermal bonding material; anddisposed along the interface between the first electrode mount and thefirst surface of the beam emitter, a sealing material for preventing orretarding movement of the thermal bonding material out of the thermalbonding layer, wherein (i) the sealing material is electricallyconductive, (ii) the sealing material directly contacts at least aportion of an external surface of the first electrode mount, (iii) thesealing material directly contacts at least a portion of an externalsurface of the beam emitter, and (iv) the sealing material covers anentirety of the thermal bonding layer at the interface between the firstelectrode mount and the first surface of the beam emitter, whereby thethermal bonding layer is unexposed and surrounded on all sides by thesealing material, the first electrode mount, and the beam emitter. 2.The laser apparatus of claim 1, wherein the thermal bonding materialcomprises indium.
 3. The laser apparatus of claim 1, wherein the sealingmaterial comprises at least one of copper, aluminum, nickel, orchromium.
 4. The laser apparatus of claim 1, wherein the sealingmaterial directly contacts an entirety of the external surface of thefirst electrode mount that is not in contact with the thermal bondinglayer.
 5. The laser apparatus of claim 1, wherein the sealing materialdirectly contacts an entirety of the external surface of the beamemitter except for (i) portions thereof in contact with the thermalbonding layer and (ii) a portion of the beam emitter from which one ormore beams are emitted.
 6. The laser apparatus of claim 1, furthercomprising: a second electrode mount (i) disposed proximate the secondsurface of the beam emitter and (ii) electrically insulated from thefirst electrode mount except for any electrical connection through thebeam emitter; a second thermal bonding layer disposed along at least aportion of an interface between the second electrode mount and thesecond surface of the beam emitter, the second thermal bonding layer (i)improving thermal conduction between the second electrode mount and thebeam emitter, and (ii) comprising a second thermal bonding material; anddisposed along at least a portion of the interface between the secondelectrode mount and the second surface of the beam emitter, a secondsealing material for preventing or retarding movement of the secondthermal bonding material out of the second thermal bonding layer.
 7. Thelaser apparatus of claim 6, wherein (i) the second sealing material iselectrically conductive, (ii) the second sealing material directlycontacts at least a portion of an external surface of the secondelectrode mount, (iii) the second sealing material directly contacts atleast a portion of an external surface of the beam emitter, and (iv) thesecond sealing material covers an entirety of the second thermal bondinglayer at the interface between the second electrode mount and the secondsurface of the beam emitter, whereby the second thermal bonding layer isunexposed and surrounded on all sides by the second sealing material,the second electrode mount, and the beam emitter.
 8. The laser apparatusof claim 6, wherein the second thermal bonding material comprisesindium.
 9. The laser apparatus of claim 6, wherein the second sealingmaterial comprises at least one of copper, aluminum, nickel, orchromium.
 10. The laser apparatus of claim 1, wherein the beam emittercomprises a diode bar emitting a plurality of discrete beams.
 11. Awavelength beam combining laser system comprising: a beam emitteremitting a plurality of discrete beams and having first and secondopposed surfaces; focusing optics for focusing the plurality of beamsonto a dispersive element; a dispersive element for receiving anddispersing the received focused beams; a partially reflective outputcoupler positioned to receive the dispersed beams, transmit a portion ofthe dispersed beams therethrough as a multi-wavelength output beam, andreflect a second portion of the dispersed beams back toward thedispersive element; a first electrode mount disposed proximate the firstsurface of the beam emitter; a thermal bonding layer disposed at aninterface between the first electrode mount and the first surface of thebeam emitter, the thermal bonding layer (i) improving thermal conductionbetween the first electrode mount and the beam emitter, and (ii)comprising a thermal bonding material; and disposed along at least aportion of the interface between the first electrode mount and the firstsurface of the beam emitter, a sealing material for preventing orretarding movement of the thermal bonding material out of the thermalbonding layer, wherein (i) the sealing material is electricallyconductive, (ii) the sealing material directly contacts at least aportion of an external surface of the first electrode mount, (iii) thesealing material directly contacts at least a portion of an externalsurface of the beam emitter, and (iv) the sealing material covers anentirety of the thermal bonding layer at the interface between the firstelectrode mount and the first surface of the beam emitter, whereby thethermal bonding layer is unexposed and surrounded on all sides by thesealing material, the first electrode mount, and the beam emitter. 12.The laser system of claim 11, wherein the dispersive element comprises adiffraction grating.
 13. The laser system of claim 11, wherein thethermal bonding material comprises indium.
 14. The laser system of claim11, wherein the sealing material comprises at least one of copper,aluminum, nickel, or chromium.
 15. The laser system of claim 11, furthercomprising: a second electrode mount (i) disposed proximate the secondsurface of the beam emitter and (ii) electrically insulated from thefirst electrode mount except for any electrical connection through thebeam emitter; a second thermal bonding layer disposed along at least aportion of an interface between the second electrode mount and thesecond surface of the beam emitter, the second thermal bonding layer (i)improving thermal conduction between the second electrode mount and thebeam emitter, and (ii) comprising a second thermal bonding material; anddisposed along at least a portion of the interface between the secondelectrode mount and the second surface of the beam emitter, a secondsealing material for preventing or retarding movement of the secondthermal bonding material out of the second thermal bonding layer. 16.The laser system of claim 11, wherein the sealing material directlycontacts an entirety of the external surface of the first electrodemount that is not in contact with the thermal bonding layer.
 17. Thelaser system of claim 11, wherein the beam emitter comprises a diodebar.
 18. The laser system of claim 11, wherein the sealing materialdirectly contacts an entirety of the external surface of the beamemitter except for (i) portions thereof in contact with the thermalbonding layer and (ii) a portion of the beam emitter from which theplurality of beams are emitted.
 19. The laser system of claim 15,wherein (i) the second sealing material is electrically conductive, (ii)the second sealing material directly contacts at least a portion of anexternal surface of the second electrode mount, (iii) the second sealingmaterial directly contacts at least a portion of an external surface ofthe beam emitter, and (iv) the second sealing material covers anentirety of the second thermal bonding layer at the interface betweenthe second electrode mount and the second surface of the beam emitter,whereby the second thermal bonding layer is unexposed and surrounded onall sides by the second sealing material, the second electrode mount,and the beam emitter.
 20. The laser system of claim 15, wherein thesecond thermal bonding material comprises indium.
 21. The laser systemof claim 15, wherein the second sealing material comprises at least oneof copper, aluminum, nickel, or chromium.